Precision tripod motion system with six degrees of freedom

ABSTRACT

A precision tripod motion system is provided. The tripod motion system in one example includes a bottom plate including three spaced-apart bottom single-degree-of-freedom (SDOF) hinge portions, a top plate including three spaced-apart top three-degrees-of-freedom (TDOF) joint portions, with the top plate configured to receive a workpiece, three linear actuators pivotally coupled to the three bottom SDOF hinge portions of the bottom plate and coupled to the three top TDOF joint portions of the top plate, with each linear actuator of the three linear actuators configured to change length over a linear actuation span, and a rotator component and/or a positioning table affixed to the top plate and the bottom plate. The tripod motion system is additionally coupled to a rotator component and a positioning table to provide six degrees of freedom of motion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims benefit of, and priority to, U.S.Provisional Patent Application Ser. No. 61/733,822, entitled “HybridParallel Kinematic Motion System” and filed on Dec. 5, 2012, thecontents of which are incorporated herein by reference. This patentapplication also claims benefit of, and priority to, U.S. ProvisionalPatent Application Ser. No. 61/733,834, entitled “Tripod ParallelKinematic Precision Motion System” and filed on Dec. 5, 2012, thecontents of which are incorporated herein by reference.

TECHNICAL BACKGROUND

Motion systems are mechanical systems that are used to hold and positiona workpiece, such as in manufacturing, machining, or industrialprocesses, for example. Motion systems used to position a workpiecetypically require a high degree of accuracy in order to achieve a highlyprecise positioning of the workpiece.

In order to be able to achieve a large number of working positions, amotion system may employ multiple actuator devices. The multipleactuator devices can be singly or jointly actuated in order to move andposition a platform or portion holding a workpiece. Complicated actuatorsystems lead to additive tolerances and therefore to reduced positionalaccuracy. Further, complicated interactions between components can leadto poor stability within the system.

A drawback of prior art motion systems is that motion systems employinga large number of actuator devices suffer from accumulated errortolerances, resulting in complicated motion systems that cannot providea high level of positional accuracy. Typical prior art motion systemsprovide micron order performance, at best, due to additive toleranceerrors from six moving hardware axes. Another drawback of prior artmotion systems is an inability to return to a set position whendisturbed by an external force.

OVERVIEW

A precision tripod motion system is provided. The tripod motion systemin one example includes a bottom plate including three spaced-apartsingle-degree-of-freedom (SDOF) hinge portions, a top plate includingthree spaced-apart top TDOF joint portions, with the top plateconfigured to receive a workpiece, three linear actuators pivotallycoupled to the three bottom SDOF hinge portions of the bottom plate andcoupled to the three top TDOF joint portions of the top plate, with eachlinear actuator of the three linear actuators configured to changelength over a linear actuation span, and a rotator component and/or apositioning table affixed to the top plate and the bottom plate. Thetripod motion system is additionally coupled to a rotator component anda positioning table to provide six degrees of freedom of motion.

This Overview is provided to introduce a selection of concepts in asimplified form that are further described below in the TechnicalDisclosure. It should be understood that this Overview is not intendedto identify key features or essential features of the claimed subjectmatter, nor is it intended to be used to limit the scope of the claimedsubject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary tripod parallel kinematic precision motionsystem.

FIG. 2 shows the tripod motion system wherein the top plate issubstantially horizontal.

FIG. 3 shows the tripod motion system wherein the top plate has beendisplaced vertically.

FIG. 4 shows the tripod motion system wherein the top plate has beentilted to the left.

FIG. 5 shows the tripod motion system wherein the top plate has beentilted to the right.

FIG. 6 shows an exemplary tripod parallel kinematic precision motionsystem.

FIG. 7 shows detail of an exemplary linear actuator.

FIG. 8 is a cross-section view of a linear actuator.

FIG. 9 is a cross-section view of the linear actuator.

FIG. 10 shows detail of a top TDOF joint.

FIG. 11 shows the tripod motion system in an operational environment.

FIG. 12 shows an exemplary tripod motion system that provides sixdegrees of freedom of motion.

FIG. 13 shows the tripod motion system in an operational environment.

DETAILED DESCRIPTION

The following description and associated drawings teach the best mode ofthe invention. For the purpose of teaching inventive principles, someconventional aspects of the best mode may be simplified or omitted. Thefollowing claims specify the scope of the invention. Some aspects of thebest mode may not fall within the scope of the invention as specified bythe claims. Thus, those skilled in the art will appreciate variationsfrom the best mode that fall within the scope of the invention. Thoseskilled in the art will appreciate that the features described below canbe combined in various ways to form multiple variations of theinvention. As a result, the invention is not limited to the specificexamples described below, but only by claims and their equivalents.

FIG. 1 shows an exemplary tripod parallel kinematic precision motionsystem 1. The tripod motion system 1 comprises a bottom plate 10, a topplate 40 that is generally initially parallel to the bottom plate 10 inorientation, such as where the tripod motion system 1 is not actuated,and three linear actuators 20 coupled between the top plate 40 and thebottom plate 10. A linear actuator 20 includes a bottomsingle-degree-of-freedom (SDOF) hinge 11 of the bottom plate 10 and atop three-degrees-of-freedom (TDOF) joint 30 of the top plate 40. Thetripod motion system 1 can be used to move, position, hold, and/ororient a workpiece. The three linear actuators 20 can be actuated toraise or lower the top plate 40, i.e., can move the top plate 40 along aZ-axis (see legend in the figure). The three linear actuators 20 can beactuated to tilt the top plate 40 to various degrees of incline and inany direction, i.e., can move the top plate 40 along one or more of theX-axis, the Y-axis, and/or the Z-axis.

The three linear actuators 20 can move the top plate 40 in a linearmotion D_(Z) along the Z-axis. The three linear actuators 20 can movethe top plate 40 in a rotational motion to tilt/rotate about the X-axisin a θ_(X) motion. The three linear actuators 20 can move the top plate40 in a rotational motion to tilt/rotate about the Y-axis in a θ_(Y)motion.

The three linear actuators 20 are configured to lengthen or shorten overa linear actuation span. The three linear actuators 20 can be singlyactuated, wherein only one linear actuator of the three linear actuators20 is actuated at one time. Alternatively, the three linear actuators 20can be multiply actuated, wherein two or three linear actuators areactuated at one time. The three linear actuators 20 can be actuated inthe same direction, i.e., all three linear actuators 20 could belengthened). Alternatively, the three linear actuators 20 can beactuated in opposing directions, with one or more linear actuators 20shortening and a different one or more lengthening at the same time.

The three linear actuators 20 can be actuated to move the top plate 40to a predetermined set position with respect to the bottom plate 10. Thepredetermined set position can vary according to conditions. Thepredetermined set position can vary according to the operation beingperformed by the tripod motion system 1. The predetermined set positioncan vary according to a sequence of operations being performed by thetripod motion system 1. After moving the top plate 40 to a predeterminedset position, the three linear actuators 20 can thereafter maintain thetop plate 40 at the set position.

The bottom plate 10 includes the three spaced-apart bottom SDOF hinges11. The bottom portion of a linear actuator 20 interacts with acorresponding bottom SDOF hinge 11 on the bottom plate 10. A bottom SDOFhinge 11 allows a linear actuator 20 to pivot with respect to the bottomplate 10, but only in a SDOF motion.

In the example shown, each bottom SDOF hinge 11 comprises a hinge blockor blocks 14 affixed to or formed as part of the bottom plate 10. Apivot pin 15 extends between the hinge block(s) 14. The bottom portionof the linear actuator 20 fits over the pivot pin 15, allowing thelinear actuator 20 to pivot in a SDOF pivoting motion with respect tothe bottom plate 10. The pivot pin 15 in one example is affixed to thehinge block(s) 14, wherein the bottom portion of the linear actuator 20rotates about the pivot pin 15. Alternatively, the pivot pin 15 can beaffixed to the bottom portion of the linear actuator 20, wherein thepivot pin 15 rotates within the hinge block(s) 14. Consequently, via thepivot pin 15, the linear actuator 20 can pivot with a SDOF motion andover a range of angular movement. Therefore, the linear actuator 20 canonly pivot in a planar arc with respect to the bottom plate 10.

The top plate 40 includes the three spaced-apart top TDOF joints 30 thatinteract with the three linear actuators 20. The top TDOF joints 30enable the linear actuators 20 to move with three rotational degrees offreedom with respect to the top plate 40. This includes the linearactuator 20 being able to rotate with respect to the top plate 40, pivotin a X-Z plane, and pivot in a Y-Z plane.

The ball 34 fits to a corresponding ball joint socket formed on theunderside of the top plate 40 (see FIG. 10 and the accompanying text).Each top TDOF joint 30 of the top plate 40 includes a semi-sphericalchamber 39 that receives and holds the ball 34 of the linear actuator20. Consequently, via the ball 34, the linear actuator 20 can move witha TDOF motion and over ranges of angular movement, in addition torotation of the ball 34. The linear actuator 20 therefore can rotateabout its own axis or can move in an X-Z plane or in a Y-Z plane in theexample shown, or in combinations thereof. Although a ball joint isshown in the example, it should be understood that any suitable jointmechanism with three degrees of freedom can be used, such as a cardanjoint/U-joint combined with a rotational joint, for example.

Each linear actuator 20 receives a set position signal and generates aset position for the tripod motion system 1. The set position comprisesa position that is supposed to be achieved and held by the linearactuator 20. As previously discussed, the three linear actuators 20 mayhave the same set position or may differ, depending on the desiredposition and orientation of the top plate 40. The three linear actuators20 are coupled to a control system 60 by lines 12. The lines 12communicate a set position signal or signals in some examples. The lines12 provide power to the three linear actuators 20 in some examples,wherein the provided power is used to hold or achieve a set position ineach linear actuator 20.

An actuation method for the tripod motion system 1 comprises receiving apredetermined set position to be achieved by the tripod motion system,with the predetermined set position including three set positions forthree linear actuators 20 of the tripod motion system 1, and moving alinear actuator 20 to the predetermined set position, with each linearactuator 20 of the three linear actuators being coupled to a bottom SDOFhinge 11 on the bottom plate 10 of the tripod motion system 1 and beingfurther coupled to a top TDOF joint 30 on the top plate 40 of the tripodmotion system 1.

The three linear actuators 20 can be configured to retract or extend byvery small and very precise linear extension increments. In someexamples, the three linear actuators 20 can be configured to move inretraction or extension increments that have an actuation displacementtolerance of microns or sub-microns, wherein the top plate 40 can bepositioned with a very high degree of accuracy.

The actuation tolerances of the linear actuators 120 in the tripodmotion system 1 can be less than about 1-5 microns per 100 millimeters(mm) of travel in some examples. Various calibration methods can be usedto further improve the geometric performance.

Rotational movements θ_(X) and θ_(Y) around the X-axis and the Y-axis,and linear movements along the Z-axis are decoupled in the tripod motionsystem 1. Due to the decoupled nature of the motion with respect to theX, Y, and Z axes, as well as the reduced error sources, calibration ofthe tripod motion system 1 enables sub-micron movement accuracy.

FIG. 2 shows the tripod motion system 100 wherein the top plate 140 issubstantially horizontal. As a result, the three linear actuators 120are all of substantially the same length.

FIG. 3 shows the tripod motion system 100 wherein the top plate 140 hasbeen displaced vertically, i.e., along the Z-axis. To displace the topplate 140 along the Z-axis, all three linear actuators 120 are equallylengthened or shortened. The dashed lines in the linear actuators120A-120C show the original displacement positions, wherein eachactuator is lengthened by an equal amount to vertically displace the topplate 140.

FIG. 4 shows the tripod motion system 100 wherein the top plate 140 hasbeen tilted to the left in the figure. To tilt the top plate 140, thethree linear actuators 120 can be actuated to different displacementlengths. The top plate 140 can be tilted independently of movement alongthe Z-axis, but also can be performed in conjunction with movement alongthe Z-axis. The tilt can be achieved in multiple ways. The tilt can beachieved by lengthening one or two linear actuators of the three linearactuators 120. The tilt can be achieved by shortening one or two linearactuators of the three linear actuators 120. The tilt can be achieved bylengthening one or two of the linear actuators and also shortening twoor one of the remaining linear actuators, wherein all three linearactuators may be changed from an initial length.

In the example in the figure, the linear actuator 120A has not beenchanged and is the same length as the starting position shown in FIG. 2.The linear actuator 120B has been lengthened somewhat, as indicated bythe dashed line indicating the starting length. The linear actuator 120Chas been lengthened more than the linear actuator 120B, as indicated bythe dashed line. As a result, the top plate 140 is now tilted to theleft (but the front-to-back tilt angle has not been changed). It shouldbe understood that if the actuator 120B had also been left unchanged andif only the linear actuator 120C had been lengthened, then the top plate140 would also tilt toward the front in the figure, in addition totilting to the left.

FIG. 5 shows the tripod motion system 100 wherein the top plate 140 hasbeen tilted to the right in the figure. In this example, the linearactuator 120B has not been changed and is the same length as thestarting position shown in FIG. 2. The linear actuator 120A has beenlengthened, as indicated by the dashed line indicating the startinglength. Conversely, the linear actuator 120C has been shortened, asindicated by the dashed line.

FIG. 6 shows an exemplary tripod parallel kinematic precision motionsystem 100. The tripod motion system 100 comprises a bottom plate 110, atop plate 140, and three linear actuators 120 coupled between the topplate 140 and the bottom plate 110. The tripod motion system 100 can beused to move, position, hold, and/or orient a workpiece, as previouslydiscussed.

The three linear actuators 120 can move the top plate 140 in a linearmotion D_(Z) along the Z-axis. The three linear actuators 120 can movethe top plate 140 in a rotational motion to tilt/rotate about the X-axisin a θ_(X) motion. The three linear actuators 120 can move the top plate140 in a rotational motion to tilt/rotate about the Y-axis in a θ_(Y)motion.

A linear actuator 120 includes an actuator body 121, a bottom hingeportion 116 that interacts with a bottom SDOF hinge 111 of the bottomplate 110, a ball 134 positioned at the top end of the actuator slider122 (see FIGS. 7-8), and an actuator flange 129 projecting from a topregion of the actuator slider 122. A linear actuator 120 furtherincludes a positioning actuator 124 that is configured to extend fromand retract into the actuator body 121, linearly displacing the actuatorslider 122 and the actuator flange 129. A linear actuator 120 furtherincludes one or more displacing actuators 128 that act against theactuator flange 129. The actuator flange 129 is configured to becontacted by the one or more displacing actuators 128 and receive theactuation force(s) generated by the one or more displacing actuators128. The one or more displacing actuators 128 provide a majority offorce to hold the linear actuator 120 at a set position.

The positioning actuator 124 receives a set position signal andgenerates a set position for the tripod motion system 100. The setposition comprises a position that is supposed to be achieved and heldby the linear actuator 120, i.e., the position/actuation length that thelinear actuator 120 should achieve. As previously discussed, the threelinear actuators may have the same set position or may differ, dependingon the desired position and orientation of the top plate 140. The setposition signal can be received from a controller device or otherexternal source (not shown). The set position signal can comprise anymanner of appropriate signal, including any appropriate mechanical,electrical, magnetic, optical, or pneumatic linear position signal.

The positioning actuator 124 generates an extension force that extendsor retracts the slider 122, which holds the ball 134. The positioningactuator 124 can be configured to retract or extend by very small andvery precise linear extension increments. In some examples, thepositioning actuator 124 can be configured to move in retraction orextension increments that have an actuation displacement tolerance ofmicrons or sub-microns, wherein the top plate 140 can be positioned witha very high degree of accuracy. However, the positioning actuator 124may not generate enough actuation force to hold or move the top plate140 against steady-state load forces such as gravity.

In one example, the positioning actuator 124 comprises an electricpositioning component, wherein an electric current is supplied to thepositioning actuator 124 in order to hold or move the actuator slider122. In another example, the positioning actuator 124 comprises a linearelectric motor, wherein an electric current is supplied to thepositioning actuator 124 in order to hold or move the actuator slider122 and wherein the linear electric motor is configured to move theactuator slider 122 by predetermined linear actuation increments. In yetanother example, the positioning actuator 124 comprises a motor androtational actuator device, such as a lead screw.

The positioning actuator 124 may be able to move the ball 134 to, andhold at, a predetermined extension position (or set position) when thereis no load or force on the top plate 140. In addition, the positioningactuator 124 will return to the predetermined set position if anexternal force displaces the top plate 140. However, the positioningactuator 124 is not designed to provide all of the hold or extensionforce that is generated by a linear actuator 120. Instead, thepositioning actuator 124 of a linear actuator 120 is designed to movethe ball 134 to a predetermined extension position.

The positioning actuator 124 receives a position command and moves theactuator slider 122 to a predetermined set position as given by theposition command. The position command is received from a controller orother external device, such as the positioning controller 170 of FIG.11, for example. However, the positioning actuator 124 does not exert amajority of the force needed to position or hold the top plate 140 atthe predetermined set position.

The one or more displacing actuators 128 act against the actuator flange129. The one or more displacing actuators 128 operate to provide amajority of the force that is needed to position and hold the top plate140 at the predetermined set position. The one or more displacingactuators 128 can supply more force to the top plate 140 than thepositioning actuator 124 can supply. The one or more displacingactuators 128 can provide the force without electrical power consumptionand without heating up the linear actuator 120. In addition, the one ormore displacing actuators 128 can counteract a disturbance of the topplate 140 due to external forces.

The one or more displacing actuators 128 are configured to generateactuation forces against the actuator flange 129. The one or moredisplacing actuators 128 are configured to generate actuation forcesthat add to the actuation force supplied by the positioning actuator124. The one or more displacing actuators 128 are configured to generateactuation forces that add to the actuation forced supplied by thepositioning actuator 124 in order to maintain the actuator slider 122 atthe set position that is set by the positioning actuator 124. The one ormore displacing actuators 128 are configured to support the load againstgravity. Further, the one or more displacing actuators 127 assist thepositioning actuator 124 in the event that an external force or forcesacts on the tripod motion system 100.

The one or more displacing actuators 128 extend to contact the actuatorflange 129. The one or more displacing actuators 128 generate actuationforces on the actuator flange 129 and the actuator slider 122,supporting the set position as set by the positioning actuator 124. Theone or more displacing actuators 128 generate the actuation forces basedon a pneumatic pressure, in some examples. Alternatively, in otherexamples, the one or more displacing actuators 128 can comprise magneticactuator devices or mechanical spring actuator devices, for example.

The one or more displacing actuators 128 in some examples comprisepneumatic actuators including a piston chamber, a piston configured toreciprocate within the piston chamber, and a piston rod coupled to thepiston and extending out of the pneumatic actuator 128. A pneumatic port(not shown) introduces pneumatic air into the one or more displacingactuators 128, below the internal piston, wherein the pneumatic airdisplaces the piston upward and extends the piston rod.

The amount of actuation force generated by the one or more displacingactuators 128 will depend on the pneumatic pressure provided to the oneor more displacing actuators 128 by an external pneumatic source. Thepneumatic pressure is calibrated according to the weight of the expectedload to be placed on and supported by the top plate 140. Alternatively,the pneumatic pressure is calibrated according to the weight of theexpected load on the top plate 140 minus an actuation force generated bythe positioning actuator 124. However, the actuation force generated bythe one or more displacing actuators 128 may be much greater than theactuation force generated by the positioning actuator 124, wherein theactuation force generated by the positioning actuator 124 may beneglected in choosing the pneumatic pressure.

The three linear actuators 120 do not require a large amount ofelectrical power to hold the set position. The low electrical powerconsumption of a positioning actuator 124 of a linear actuator 124minimizes heating of the linear actuator 120. The one or more displacingactuators 128 provide a majority of force to hold the linear actuator120 at a set position. The one or more displacing actuators 128 make theload essentially weightless and the positioning actuator 124 supplies anadditional force to change the position of the top plate 140 and theload. It is an advantage that the three linear actuators 120 will returnthe top plate 140 to the set position after the top plate 140 isdisturbed or displaced by an external force. It is an advantage that thethree linear actuators 120 (and the tripod motion system 100) can bedesigned and configured to achieve a sub-micron positioning accuracy ofthe top plate 140.

The bottom plate 110 includes three spaced-apart bottomsingle-degree-of-freedom (SDOF) hinges 111. The bottom hinge portion 116of a linear actuator 120 interacts with a corresponding bottom SDOFhinge 111 on the bottom plate 110. A bottom SDOF hinge 111 allows alinear actuator 120 to pivot with respect to the bottom plate 110, butonly in a SDOF motion.

In the example shown, each bottom SDOF hinge 111 comprises two hingeblocks 114 affixed to or formed as part of the bottom plate 110. A pivotpin 115 extends between the two hinge blocks 114. The bottom hingeportion 116 of the linear actuator 120 fits over the pivot pin 115,allowing the linear actuator 120 to pivot in a SDOF pivoting motion withrespect to the bottom plate 110. The pivot pin 115 in one example isaffixed to the two hinge blocks 114, wherein the bottom hinge portion116 of the linear actuator 120 rotates about the pivot pin 115.Alternatively, the pivot pin 115 can be affixed to the bottom hingeportion 116, wherein the pivot pin 115 rotates within the two hingeblocks 114. Consequently, via the pivot pin 115, the linear actuator 120can pivot with a SDOF motion and over a range of angular movement.Therefore, the linear actuator 120 can only pivot in a planar arc withrespect to the bottom plate 110. Alternatively, the bottom SDOF hinges111 can comprise any mechanism that allows movement in a single degreeof freedom, such as bearings, for example.

The top plate 140 includes three spaced-apart topthree-degree-of-freedom (TDOF) joints 130 that interact with the threelinear actuators 120. The top TDOF joints 130 enable the linearactuators 120 to move with three rotational degrees of freedom withrespect to the top plate 140. This includes the linear actuator 120being able to rotate with respect to the top plate 140, pivot in a X-Zplane, and pivot in a Y-Z plane.

The ball 134 fits to a corresponding ball joint socket formed on theunderside of the top plate 140 (see FIG. 10 and the accompanying text).Each top TDOF joint 130 of the top plate 140 includes a semi-sphericalchamber 139 that receives and holds the ball 134 of the linear actuator120. Consequently, via the ball 134, the linear actuator 120 can movewith a TDOF motion and over ranges of angular movement, in addition torotation of the ball 134. The linear actuator 120 therefore can rotateabout its own axis or can move in an X-Z plane or in a Y-Z plane in theexample shown, or in combinations thereof. Alternatively, the top TDOFjoints 130 can comprise cardan joints/U-joints combined with arotational joint or any other suitable mechanism that allows threedegrees of freedom of movement.

The actuation tolerances in the linear actuators 120 of the tripodmotion system 100 can be less than about 1-5 microns per 100 millimeters(mm) of travel in some examples. Various calibration methods can be usedto further improve the geometric performance.

Rotational movements around the X-axis and the Y-axis, and linearmovements along the Z-axis are decoupled in the tripod motion system100. Due to the decoupled nature of the motion with respect to the X, Y,and Z axes, as well as the reduced error sources, calibration of thetripod motion system 100 enables sub-micron movement accuracy.

An actuation method for the tripod motion system 100 comprises receivinga predetermined set position to be achieved by the tripod motion system,with the predetermined set position including three set positions forthree linear actuators of the tripod motion system, moving a positioningactuator of a linear actuator substantially to the correspondingpredetermined set position, with each linear actuator of the threelinear actuators being coupled to a bottom single-degree-of-freedom(SDOF) hinge on a bottom plate of the tripod motion system and beingfurther coupled to a top three-degrees-of-freedom (TDOF) joint on a topplate of the tripod motion system, and moving one or more displacingactuators of the linear actuator to boost the linear actuator and tohold the linear actuator at the predetermined set position, with the oneor more displacing actuators of the linear actuator providing a majorityof a displacement force generated by the linear actuator.

FIG. 7 shows detail of an exemplary linear actuator 120. The linearactuator 120 includes the bottom hinge portion 116 that fits around thepivot pin 115. Connectors 113 extend from the actuator body 121 in theregion of the bottom hinge portion 116. The connectors 113 in oneexample comprise electrical and pneumatic connectors that supplyelectrical power and pneumatic power to the linear actuator 120. Inaddition, the connectors 113 can provide control signals to the linearactuator 120. The figure shows the ball 134 that comprises a portion ofthe top TDOF joint 130. The figure also shows the actuator flange 129.The actuator flange 129 is affixed to the top region of the actuatorslider 122. The actuator flange 129 can be affixed to the actuatorslider 122 in any suitable manner, including using adhesives or bondingagents, welds, clips, latches, or fasteners. In the example, the one ormore displacing actuators 128 comprise two displacing actuators 128. Thetwo displacing actuators 128 in the figure are not currently pressurizedwith pneumatic air, and consequently the two displacing actuators 128 donot extend upwards and contact the actuator flange 129.

FIG. 8 is a cross-section view AA of the linear actuator 120 of FIG. 7.It can be seen from the figure that the bottom hinge portion 116includes a pin aperture 112 for receiving the pivot pin 115. The pinaperture 112 further includes a compression gap 118 that allows the pinaperture 112 to be constricted, wherein the bottom hinge portion 116 canbe clamped onto the pivot pin 115. The pin aperture 112 further includesa threaded bore 117 and countersink 119 for receiving a threadedfastener (not shown), wherein the threaded fastener can be manipulatedto constrict the compression gap 118.

The actuator body 121 includes a displacing actuator chamber 234 thatreceives the one or more displacing actuators 128. The number ofdisplacing actuators 128 can be chosen according to the desireddisplacing actuator force to be placed on the actuator flange 129 insome examples, wherein the number of displacing actuators can beincreased where an increased displacing actuator force is desired. Apneumatic conduit 235 passes into the displacing actuator chamber 234and is coupled to the one or more displacing actuators 128. Thepneumatic conduit 235 provides pneumatic pressure to the one or moredisplacing actuators 128. The piston rods of the one or more displacingactuators 128 extend up through the top of the actuator body 121 and cancontact the underside of the actuator flange 129, supplying a displacingforce to the actuator slider 122.

The actuator body 121 further includes a positioning actuator chamber241 that receives the positioning actuator 124. The positioning actuatorchamber 241 can comprise a separate chamber from the displacing actuatorchamber 234, or can be at least partially open to the displacingactuator chamber 234.

The positioning actuator 124 in the example shown comprises a linearelectric motor. The positioning actuator 124 includes a magnetic body246 affixed to the actuator slider 122 and a stationary componentcomprising a coil assembly 247 (see FIG. 9) affixed to the actuator body121. The coil assembly 247 acts on the magnetic body 246 when energized.The coil assembly 247 can cause the actuator slider 122 to be extendedfarther from the actuator body 121. Conversely, the coil assembly 247can cause the actuator slider 122 to be further retracted into theactuator body 121. Electrical conductors (not shown), such as wires orcables, can extend into the positioning actuator chamber 241 to the coilassembly 247.

The positioning actuator 124 further includes a positional feedbackdevice 249 that generates a positional signal that is provided to thecoil assembly 247 (or is provided to a positioning controller 170 thatoperates the coil assembly 247, see FIG. 11). The positional feedbackdevice 249 generates a linear positional signal that is used to actuatethe positioning actuator 124. The positional feedback device 249generates the positional signal based on the linear position of theactuator slider 122 (see FIG. 9 and the accompanying discussion below).The positional feedback device 249 is able to sense and move to positionincrements that have an error tolerance of microns or sub-microns.

In one example, the positional feedback device 249 comprises a magneticsensor, including a Hall Effect sensor. Alternatively, the positionalfeedback device 249 can comprise an optical, electrical, or mechanicalsensor or other position sensor that generates a suitable positionalsignal.

FIG. 9 is a cross-section view BB of the linear actuator 120 of FIG. 7.This figure shows the components of the positioning actuator 124 in oneexample. The positioning actuator 124 in this example includes theactuator slider 122, a magnetic body 246 affixed to the actuator slider122, and a coil assembly 247 that corresponds in shape to the magneticbody 246. The coil assembly 247 acts on the magnetic body 246 whenenergized and generates magnetic force on the magnetic body 246, whereinthe magnetic body 246 moves the actuator slider 122.

Roller bearings 501 are located on the sides of the actuator slider 122.The roller bearings 501 allow the actuator slider 122 to move smoothlyup and down within the actuator body 121.

The linear actuator 120 further includes an encoder grating 248 affixedto the actuator slider 122. A positional feedback device 249 is affixedto the actuator body 121 and interacts with the encoder grating 248 togenerate a linear positional feedback signal. The positional feedbacksignal corresponds to the position of the actuator slider 122.

FIG. 10 shows detail of a top TDOF joint 130. Each top TDOF joint 130includes a semi-spherical ball chamber 139 formed in the top plate 140and a ball retainer plate 136 held to the top plate 140. The ballretainer plate 136 is affixed to the top plate 140. The ball retainerplate 136 can be affixed to the top plate 140 in any suitable manner,including using adhesives or bonding agents, welds, clips, latches, orfasteners. The ball retainer plate 136 also includes a semi-sphericalchamber, wherein the semi-spherical chamber 139 and the ball retainerplate 136 together trap and hold the ball 134 of the linear actuator120. The ball retainer plate 136 includes an opening 137 that allows theactuator slider 122 to move over a predetermined range of motions as theball 134 rotates within the semi-spherical chamber 139 of the top plate140. As a result, the linear actuator 120 can move with a TDOF motionand over ranges of angular movement, in addition to rotation of the ball134. The linear actuator 120 therefore can rotate about its own axis orcan move in an X-Z plane or in a Y-Z plane in the example shown, or incombinations thereof.

FIG. 11 shows the tripod motion system 100 in an operationalenvironment. The tripod motion system 100 further includes a positioningcontroller 170 that is coupled to the positioning actuators 124 of thethree linear actuators 120. The positioning controller 170 receives thepositional signal that is generated by the positional feedback device249. The positioning controller 170 processes the positional signal andtransmits a control signal to the coil assembly. The control signaloperates the coil assembly to put the positioning actuator 124 at thepredetermined set position.

The tripod motion system 100 further includes a displacing controller175 that operates the one or more displacing actuators 128. In someexamples, the positioning controller 170 and the displacing controller175 can comprise sub-components of a controller that controls allaspects of the tripod motion system 100, such as in the control system60 of FIG. 1. The displacing controller 175 can includes a pneumatic airsource coupled to the one or more displacing actuators 128 of each ofthe three linear actuators 120. The displacing controller 175 canregulate the provision of pneumatic air to the one or more displacingactuators 128. The displacing controller 175 can include variouspneumatic components, including a cut-off valve, a pressure regulator,air dryers or filters, and any other needed components.

The displacing controller 175 in one example includes a pressureregulator 179 that supplies a substantially fixed pneumatic pressure tothe one or more displacing actuators 128. The substantially fixedpneumatic pressure comprises a pneumatic pressure that is selected toenable the one or more displacing actuators 128 to hold the linearactuator 120 at the predetermined set position. The substantially fixedpneumatic pressure will be satisfactory for maintaining a predeterminedset position wherein a load applied to the top plate 140 is relativelyunvarying.

The displacing controller 175 in another example includes a controllablepressure regulator 179 that supplies a controllable pneumatic pressureto the one or more displacing actuators 128. The controllable pneumaticpressure comprises a pneumatic pressure that can be varied as needed inorder to enable the one or more displacing actuators 128 to hold thelinear actuator 120 at the predetermined set position. The controllablepneumatic pressure can be varied to accommodate loads that varydynamically in weight. Alternatively, the pressure regulator 179 can bereplaced by counterbalances.

The three linear actuators 120 are controlled by the positioningcontroller 170. The linear actuator motion can be independent orcoordinated. Coordinated motion means that all linear actuators 120 aremoved strategically in synchronized fashion with respect to time, notnecessarily with respect to the same position, such that the threelinear actuators 120 move the top plate 140 in a clearly defined andintended motion in the degrees of freedom in the linear motion D_(Z) andin the rotational motions θ_(X), and θ_(Y). In order to have the linearactuators 120 move in the coordinated motion, the positioning controller170 can calculate kinematic relationships of the linear actuators 120based on theoretical or calibrated joint locations 34 and 15 (or 130 and111). The kinematic equations can be processed in both a forward andinverse kinematic method to ensure both the ending location and the pathtaken to achieve the ending location are controlled and optimized inreal time. The forward kinematics take the existing locations of thelinear actuators 120 determined by the positional feedback device 249and calculate the coordinate system axes of the top plate 140. Theinverse kinematic equations take the desired end points in thecoordinate system axes and calculate the desired position of each linearactuator which is used to drive the tripod motion system to thatposition. Both sets of kinematics are used to provide optimumperformance, but both sets are not required.

FIG. 12 shows an exemplary tripod motion system 300 that provides sixdegrees of freedom of motion. In addition to the previously recitedcomponents, the tripod motion system 300 includes a XY positioning table325 affixed to one of the bottom plate 110 or the top plate 140 and arotator component 313 affixed to one of the top plate 140 or the bottomplate 110. However, in some examples, both of the positioning table 325and the rotator component 313 can be affixed to the top plate 140 orboth can be affixed to the bottom plate 110. A workpiece can be affixedto the rotator component 313. The rotator component 313 and thepositioning table 325 can be coupled to a controller that operates thetripod motion system 300, as previously discussed.

The rotator component 313 can rotate about the Z-axis in a θ_(Z) motion.The three linear actuators 120 can move the top plate 140 in a linearmotion D_(Z) along the Z-axis. The three linear actuators 120 can movethe top plate 140 in a rotational motion to tilt/rotate about the X-axisin a θ_(X) motion. The three linear actuators 120 can move the top plate140 in a rotational motion to tilt/rotate about the Y-axis in a θ_(Y)motion. The positioning table 325 can move the bottom plate 110 in alinear motion D_(X) along the X-axis. The positioning table 325 can movethe bottom plate 110 in a linear motion D_(Y) along the Y-axis.

The rotator component 313 is configured to receive the workpiece androtate the workpiece. The rotator component 313 is affixed to the topplate 140 and is configured to rotate about a Z-axis of the tripodmotion system 300. The rotator component 313 can rotate through anyamount of rotational displacement. The rotator component 313 can includea rotational feedback device (not shown). The rotational feedback deviceprovides θ_(Z) rotational position information to a rotator controller184 (see FIG. 13).

The positioning table 325 is affixed to the bottom plate 110. Thepositioning table 325 is configured to move the bottom plate 110 withrespect to an X-axis and with respect to a Y-axis. The positioning table325 is configured to move the bottom plate 110 in an X-direction. Thepositioning table 325 is configured to move the bottom plate 110 in aY-direction. It should be understood that the positioning table 325 cansimultaneously move the bottom plate 110 in both the X-direction and inthe Y-direction.

The positioning table 325 in the example shown includes a bottom layer320, a middle layer 322, and a top layer 326. Translation mechanisms331, 332, and 333 are disposed between the bottom layer 320 and themiddle layer 322. The translation mechanisms 331, 332, and 333 caninclude a rail or rails for allowing translation of the middle layer 322in a Y-direction with respect to the bottom layer 320. The translationmechanisms 331, 332, and 333 can include a power transmission device ordevices for translating the middle layer 322 in the Y-direction.Likewise, translation mechanisms 337, 338, and 339 are disposed betweenthe middle layer 322 and the top layer 326. The translation mechanisms337, 338, and 339 include a guide structure or structures for allowingtranslation motion of the top layer 326 in an X-direction with respectto the middle layer 322. The translation mechanisms 337, 338, and 339can include a power transmission device or devices for translating thetop layer 326 in the X-direction. In some examples, the translationmechanisms 337 and 339 comprise bearings and the translation mechanism338 comprises a motor and actuator mechanism.

In addition, the positioning table 325 can include a position feedbackdevice (not shown). The position feedback device provides X-axis andY-axis positional feedback information to a table controller 186 (seeFIG. 13).

It can be seen from the figure that the tripod motion system 300 canprovide six degrees of freedom of movement to a workpiece affixed to therotator component 313. The tripod motion system 300 can move theworkpiece straight up and down, in a Z-direction. The tripod motionsystem 300 can move the workpiece front-to-back, in a Y-direction. Thetripod motion system 300 can move the workpiece side-to-side, in anX-direction. The tripod motion system 300 can rotate the workpiecearound the Z-axis. The tripod motion system 300 can tilt the workpiecewith respect to the X-axis. The tripod motion system 300 can tilt theworkpiece with respect to the Y-axis.

FIG. 13 shows a tripod motion system 1200 in an operational environment.The tripod motion system 1200 further includes a tripod controller 173that is coupled to the three linear actuators 120, a rotator controller184 that is coupled to the rotator component 313, and a table controller186 that is coupled to the positioning table 325. The tripod controller173 controls actuations of the three linear actuators 120 and cangenerate the rotational movements θ_(X) and θ_(Y) and can generate thelinear movement D_(Z). The rotator controller 184 controls actuation ofthe rotator component 313 and can generate the rotational movementθ_(Z). The table controller 186 controls actuations of the positioningtable 325 and can generate the linear movements D_(X) and D_(Y).However, it should be understood that the tripod controller 173, therotator controller 184, and the table controller 186 could alternativelybe combined into a single controller or could be incorporated into othersystems or components.

In some examples, an actuation method for a tripod motion systemcomprises the tripod motion system receiving a predetermined setposition to be achieved by the tripod motion system, with thepredetermined set position including three set positions for threelinear actuators of the tripod motion system. The method furthercomprises the tripod motion system moving a positioning actuator of alinear actuator substantially to the corresponding predetermined setposition. Each linear actuator of the three linear actuators is coupledto a bottom single-degree-of-freedom (SDOF) hinge on a bottom plate ofthe tripod motion system and is further coupled to a topthree-degrees-of-freedom (TDOF) joint on a top plate of the tripodmotion system. The method further comprises the tripod motion systemmoving one or more displacing actuators of the linear actuator to boostthe linear actuator and to hold the linear actuator at the predeterminedset position, with the one or more displacing actuators of the linearactuator providing a majority of a displacement force generated by thelinear actuator. The method further comprises the tripod motion systemrotating a rotator component affixed to the top plate. The rotatorcomponent is adapted to receive and rotate a workpiece about a Z-axis ofthe tripod motion system. The method further comprises the tripod motionsystem translating a positioning table along one or both of an X-axisand a Y-axis. The bottom plate is affixed to and moved by thepositioning table.

The above description and associated figures teach the best mode of theinvention. The following claims specify the scope of the invention. Notethat some aspects of the best mode may not fall within the scope of theinvention as specified by the claims. Those skilled in the art willappreciate that the features described above can be combined in variousways to form multiple variations of the invention. As a result, theinvention is not limited to the specific embodiments described above,but only by the following claims and their equivalents.

What is claimed is:
 1. A tripod motion system, comprising: a bottomplate including three spaced-apart single-degree-of-freedom (SDOF)hinges; a top plate including three spaced-apart three-degree-of-freedom(TDOF) joints, with the top plate configured to receive a workpiece; andthree linear actuators, with each of the three linear actuatorspivotally coupled to an associated one of the three SDOF hinges of thebottom plate and coupled to an associated one of the three TDOF jointsof the top plate, and configured to change length over a linearactuation span, wherein each of the three linear actuators return thetop plate to a predetermined set position after being displaced by anexternal force; a rotator component affixed to one of the top plate orthe bottom plate, with the rotator component configured to rotate abouta Z-axis of the tripod motion system; wherein the tripod motion systemis configured to achieve a sub-micron positioning accuracy; wherein eachof the three linear actuators comprises: a ball coupled to theassociated one of the three TDOF joints; and a positioning actuatorconfigured to move the ball to a predetermined set position prior to thereturn of the top plate to the predetermined set position of the topplate.
 2. The tripod motion system of claim 1, with the three linearactuators and the rotator component providing four degrees of freedom ofmovement.
 3. The tripod motion system of claim 1, further comprising apositioning table affixed to one of the bottom plate or the top plate,with the positioning table configured to move linearly with respect toan X-axis and move linearly with respect to a Y-axis, and with the threelinear actuators, the rotator component, and the positioning tableproviding six degrees of freedom of movement.
 4. The tripod motionsystem of claim 1, with a TDOF joint of each linear actuator of thethree linear actuators and an associated TDOF joint of the top platecomprising a ball joint; with each of the SDOF hinges of the bottomplate including a pivot pin; and with a bottom SDOF hinge of each linearactuator of the three linear actuators interacting with an associatedone of the pivot pins, wherein each linear actuator of the three linearactuators can pivot in a SDOF motion on the associated one of the pivotpins.
 5. The tripod motion system of claim 1, with at least one linearactuator of the three linear actuators comprising: the positioningactuator configured to extend or retract the at least one linearactuator to a predetermined set position; and one or more displacingactuators configured to boost a positioning actuator force and hold theat least one linear actuator at the predetermined set position, with theone or more displacing actuators of the at least one linear actuatorproviding a majority of a displacement force generated by the at leastone linear actuator.
 6. The tripod motion system of claim 1, with atleast one linear actuator of the three linear actuators comprising: thepositioning actuator being an electric positioning actuator, theelectric positioning actuator configured to extend or retract the atleast one linear actuator to a predetermined set position; and one ormore pneumatic displacing actuators configured to boost the electricpositioning actuator and hold the at least one linear actuator at thepredetermined set position, with the one or more displacing actuators ofthe at least one linear actuator providing a majority of a displacementforce generated by the at least one linear actuator.
 7. The tripodmotion system of claim 6, further comprising a pressure regulator thatsupplies a substantially fixed pneumatic pressure to the one or moredisplacing actuators.
 8. The tripod motion system of claim 6, furthercomprising a controllable pressure regulator that supplies acontrollable pneumatic pressure to the one or more displacing actuators.9. A tripod motion system, comprising: a bottom plate including threespaced-apart single-degree-of-freedom (SDOF) hinges; a top plateincluding three spaced-apart three-degree-of-freedom (TDOF) joints, withthe top plate configured to receive a workpiece; and three linearactuators, with each of the three linear actuators pivotally coupled toan associated one of the three SDOF hinges of the bottom plate andcoupled to an associated one of the three TDOF joints of the top plate,and configured to change length over a linear actuation span, whereineach of the three linear actuators return the top plate to apredetermined set position after being displaced by an external force; apositioning table affixed to one of the bottom plate or the top plate,with the positioning table configured to move linearly with respect toan X-axis and move linearly with respect to a Y-axis; wherein the tripodmotion system is configured to achieve a sub-micron positioningaccuracy; wherein each of the three linear actuators comprises: a ballcoupled to the associated one of the three TDOF joints; and apositioning actuator configured to move the ball to a predetermined setposition prior to the return of the top plate to the predetermined setposition of the top plate.
 10. The tripod motion system of claim 9, withthe three linear actuators and the positioning table providing fivedegrees of freedom of movement.
 11. The tripod motion system of claim 9,further comprising a rotator component affixed to one of the top plateor the bottom plate, with the rotator component configured to rotateabout a Z-axis of the tripod motion system, and with the three linearactuators, the positioning table, and the rotator component providingsix degrees of freedom of movement.
 12. The tripod motion system ofclaim 9, with a TDOF joint of each linear actuator of the three linearactuators and an associated TDOF joint of the top plate comprising aball joint; with each of the SDOF hinges of the bottom plate including apivot pin; and with a bottom SDOF hinge of each linear actuator of thethree linear actuators interacting with an associated one of the pivotpins, wherein each linear actuator of the three linear actuators canpivot in a SDOF motion on the associated one of the pivot pins.
 13. Thetripod motion system of claim 9, with at least one linear actuator ofthe three linear actuators comprising: the positioning actuatorconfigured to extend or retract the at least one linear actuator to apredetermined set position; and one or more displacing actuatorsconfigured to boost a positioning actuator force and hold the at leastone linear actuator at the predetermined set position, with the one ormore displacing actuators of the at least one linear actuator providinga majority of a displacement force generated by the at least one linearactuator.
 14. The tripod motion system of claim 9, with at least onelinear actuator of the three linear actuators comprising: thepositioning actuator being an electric positioning actuator, theelectric positioning actuator configured to extend or retract the atleast one linear actuator to a predetermined set position; and one ormore pneumatic displacing actuators configured to boost the electricpositioning actuator and hold the at least one linear actuator at thepredetermined set position, with the one or more displacing actuators ofthe at least one linear actuator providing a majority of a displacementforce generated by the at least one linear actuator.
 15. The tripodmotion system of claim 14, further comprising a pressure regulator thatsupplies a substantially fixed pneumatic pressure to the one or moredisplacing actuators.
 16. The tripod motion system of claim 14, furthercomprising a controllable pressure regulator that supplies acontrollable pneumatic pressure to the one or more displacing actuators.17. An actuation method for a tripod motion system with six degrees offreedom, comprising: in the tripod motion system, receiving apredetermined set position to be achieved by the tripod motion system,with the predetermined set position including three set positions forthree linear actuators of the tripod motion system; in the tripod motionsystem, moving a positioning actuator of at least one linear actuator ofthe three linear actuators substantially to the correspondingpredetermined set position, with each linear actuator of the threelinear actuators being coupled to an associated single-degree-of freedom(SDOF) hinge of three SDOF hinges on a bottom plate of the tripod motionsystem and being further coupled to an associatedthree-degrees-of-freedom (TDOF) joint of three TDOF joints on a topplate of the tripod motion system; in the tripod motion system, movingone or more displacing actuators of the at least one linear actuator toboost the at least one linear actuator and to hold the at least onelinear actuator at the predetermined set position, with the one or moredisplacing actuators of the at least one linear actuator providing amajority of a displacement force generated by the at least one linearactuator; in the tripod motion system a ball coupled to the associatedone of the three TDOF joints of each of the three linear actuators,moving the ball to a predetermined set position prior to the return ofthe tripod motion system to the predetermined set of the tripod motionsystem; in the tripod motion system, rotating a rotator componentaffixed to the top plate, wherein the rotator component is adapted toreceive and rotate a workpiece about a Z-axis of the tripod motionsystem; and in the tripod motion system, translating a positioning tablealong one or both of an X-axis and a Y-axis, wherein the bottom plate isaffixed to and moved by the positioning table.
 18. The actuation methodof claim 17, with the three linear actuators, the rotator component, andthe positioning table providing six degrees of freedom of movement.